The natural capability of the human body to regenerate bone defects is not sufficient. Therefore, for the human body is typically not possible to restore a fracture on its own. Medical implants are useful in providing sufficient stability for the fracture and support the curing process.
In cases where the bone damage is too severe, bone cements may also be applied to stabilize implants and thereby support the curing of the defect.
Bone cements may act as an artificial “linker” between the natural bone and the implant. Usually, bone cements are classified into two general classes, so called PMMA bone cements (Poly Methyl Methacrylates) and calcium phosphate based cements.
Since the discovery of the calcium phosphate based cements in the mid 1980ies, various formulations have been developed. The underlying principle of these materials is that a mixture of one or more calcium salts with water or an aqueous solution forms a cement which due to a dissolution and precipitation process sets. The setting typically takes place under physiological conditions. The final reaction product (after setting) is typically a hydroxyapatite that is very similar to the biological material in terms of crystallinity and non-stoichiometry.
One of the main advantages of the calcium phosphate foams is their excellent biocompatibility and bioactivity. Moreover, the foam is capable of adapting to the geometry of the defect.
The properties of the resulting calcium phosphate foam (bone foam) can be adjusted by modifying various parameters such as the chemical composition of the starting material, the relative proportion of the constituents, additives (such as seeds, accelerants, retardants, etc.), particle size, pH value, liquid to powder ratio, temperature, humidity or the like.
The porosity of the bone foam is a further important parameter and is also important for the durability of e.g. implants. On the one hand, a high porosity is desired to allow for space for newly formed bone tissue. On the other hand, the higher the porosity of the resulting material, the smaller is its breaking strength.
Moreover, the handling of the current products is far from ideal. The application of bone cements into a void for example of an osteoporotic bone is very difficult as the cement paste is made outside the application site and subsequently applied into the damaged bone. Therefore, it is very difficult to apply the foam into small cavities which cannot be reached by the instrument with which the paste is applied to the damaged bone.
EP 1 787 626 describes an injectable self setting calcium phosphate foam for use as biomaterial. The foam is prepared by agitation and mechanical whipping and may subsequently be applied.
Particles for incorporation of particulate components in a calcium phosphate cement are for example known from U.S. Pat. No. 5,525,148 issued to Chow et al., U.S. Pat. No. 5,820,632 issued to Constantz et al., or JP 5,023,387 issued to Hirano et al.
One of the problems associated with the calcium phosphate bone foams of the prior art is that they are prepared extra corporally and only after preparation applied to the corresponding site of application in the body by manually controlled means, e.g. a syringe. For small application sites or complex geometric forms there is a need for an improved application of the foams and/or foams which are instantly applied to the application site after preparation (“direct to patient application”).